JP7460015B2 - Precious metal adsorbent, precious metal recovery method, and precious metal adsorbent regeneration method - Google Patents

Description

The present invention relates to a precious metal adsorbent, a method for recovering precious metals, and a method for regenerating a precious metal adsorbent.
This application claims priority based on Japanese Patent Application No. 2021-050484 filed on March 24, 2021, the contents of which are incorporated herein by reference.

Precious metals such as gold, silver, and platinum have been highly valued since ancient times due to their rarity and durability. In modern times, they also play an important role in industrial applications such as catalysts. However, for example, the amount of gold mined is increasing year by year, and it is said that the mineable years are about 18 years away as of 2013. In addition, along with social unrest, its price has been fluctuating wildly but has been on an upward trend in the long term.

On the other hand, recent precision equipment contains large amounts of gold and silver, and this waste is sometimes described as urban mines. Japan's urban mines are estimated to contain 16% of the existing gold reserves and 22% of the silver in 2006, and their effective utilization is an important issue.

Conventional methods for recovering precious metals include solvent extraction and ion exchange resin methods. Solvent extraction requires complicated steps, and disposal of the large amounts of waste liquid generated is problematic. On the other hand, ion exchange resin methods require the use of synthetic resins with specific functional groups and involve a complicated desorption process from the resin, which can make them expensive.

As an alternative to this, various new forms of noble metal adsorption materials have been studied in recent years. It has been disclosed that gold (Au), silver (Ag), and palladium (Pd) can be adsorbed using an insoluble gel formed by crosslinking (Patent Document 1).
Further, as another means, recovery of precious metals using a porous porphyrin polymer represented by a specific structural formula is disclosed. This method is said to have adsorption performance sufficient to concentrate precious metals even at low concentrations such as seawater, and is said to be reusable as an adsorbent by acid treatment after adsorption (patented). Reference 2).

In addition, there are reports of the use of copper sulfide as an adsorbent for mercury (Patent Document 3), and of a hydrogel based on a thiourea skeleton, an organic sulfur compound, as an adsorbent for gold, platinum, and palladium (Patent Document 4).

JP 2019-72722 A JP2019-104911A JP 2019-171257 A Japanese Patent Application Publication No. 2011-183376

However, Patent Document 1 discloses that a gel made from polyphenol derived from grape seeds selectively adsorbs gold, but there is no quantitative knowledge of the amount of gold adsorbed or a method for recovering adsorbed gold. There is no knowledge regarding this.
In addition, in Patent Document 2, the difficulty in synthesizing the porous porphyrin polymer that is the adsorbent is high, and in order to recover gold after adsorption by acid treatment, dissolved gold ions are reduced to zero-valent gold. The gold refund process is complicated. Furthermore, when the adsorption target is gold ions, it is said that 1.617 mg per 1 mg of porphyrin polymer can be adsorbed, and in the case of platinum ions, 0.1968 mg per 1 mg of porphyrin polymer can be adsorbed, but in order to achieve even higher adsorption capacity. It is necessary to irradiate light for a long time of about 48 hours, and adsorption performance using a shorter and simpler method is desired.
Further, Patent Document 3 does not disclose the use of copper sulfide to adsorb noble metals other than mercury, or the adsorption performance in that case. Even in Patent Document 4, when a hydrogel having a thiourea skeleton, which is an organic sulfur compound, is used, the adsorption amount of gold, etc. is not sufficient, and there is no disclosure of the adsorption limit concentration, so there is room for improvement.

The present invention aims to provide a precious metal adsorbent, a precious metal recovery method, and a method for regenerating a precious metal adsorbent that can easily recover precious metals while achieving high adsorption performance for precious metals.

As a result of extensive research, the inventors have found that when metal sulfides are used as precious metal adsorbents, particularly molybdenum disulfide particles, high adsorption performance can be achieved due to the selectivity of the metal sulfides to precious metals. In particular, when molybdenum disulfide particles are used as a gold adsorbent, the selectivity of the molybdenum disulfide particles to gold is extremely high, and the amount of precious metal adsorbed per unit mass of the molybdenum disulfide particles is significantly increased compared to conventional precious metal adsorbents, thereby improving adsorption performance.

In addition, if molybdenum disulfide particles are produced using the "nm-sized molybdenum oxide fine particles" owned by the present applicant as a raw material, it is possible to produce molybdenum disulfide particles using the "nm-sized molybdenum oxide fine particles" technology owned by the present applicant. Nanometer-sized molybdenum disulfide particles with a plate-like structure and a large surface area per unit weight, which is difficult to achieve, are obtained. Therefore, when these molybdenum disulfide particles are used as a noble metal adsorbent, especially a gold adsorbent, the gold adsorption rate and amount of gold adsorption can be significantly increased due to the large specific surface area of the molybdenum disulfide particles and the affinity between gold and sulfur. I found out.

Furthermore, after adsorbing the noble metal on the noble metal adsorbent, the noble metal adsorbent is heated in the presence of oxygen to volatilize it, thereby making it possible to recover the noble metal in a zero-valent state without changing the valence of the noble metal. For this reason, it has been found that the reduction treatment of the noble metal element is no longer necessary, the precious metal can be easily recovered, and the environmental burden associated with the reduction treatment can be eliminated. In particular, we found that when molybdenum disulfide particles are heated in the presence of oxygen after noble metals are adsorbed onto the molybdenum disulfide particles, the noble metals can be recovered more easily due to the high volatility of molybdenum oxide particles in which molybdenum disulfide is oxidized. I found it.

In addition, after recovering the volatilized metal oxide, the metal oxide can be sulfidized by, for example, heating in the presence of a sulfur source to obtain metal sulfides. This makes it possible to easily regenerate the metal sulfides as precious metal adsorbents, and the researchers found that the consumption of metal resources can be reduced by reusing the metal sulfides obtained.

That is, the present invention provides the following configuration.
[1] A noble metal adsorbent containing metal sulfide.

[2] The noble metal adsorbent according to [1] above, wherein the metal sulfide is composed of molybdenum disulfide particles.

[3] The noble metal adsorbent according to the above [2], wherein the median diameter _D50 of the molybdenum disulfide particles measured by a dynamic light scattering method is 10 nm or more and 1000 nm or less.

[4] The noble metal according to [2] or [3] above, wherein the primary particle shape of the molybdenum disulfide particles is disc-shaped, ribbon-shaped, or sheet-shaped, and the thickness is in the range of 3 to 100 nm. adsorbent.

[5] The noble metal adsorbent according to any one of [2] to [4] above, wherein the molybdenum disulfide particles have a specific surface area of 10 m ² /g or more as measured by the BET method.

[6] In the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the K-absorption edge of molybdenum of the molybdenum disulfide particles, the intensity I of the peak due to Mo-S and the Mo-Mo The noble metal adsorbent according to any one of [2] to [5] above, wherein the ratio (I/II) to the resulting peak intensity II is larger than 1.0.

[7] The molybdenum disulfide particles have a 2H crystal structure and a 3R crystal structure of molybdenum disulfide,
In a profile obtained by powder X-ray diffraction (XRD) of the molybdenum disulfide particles using Cu-Kα radiation as an X-ray source, a peak near 39.5° and a peak near 49.5° are derived from the 2H crystal structure, and a peak near 32.5°, a peak near 39.5°, and a peak near 49.5° are derived from the 3R crystal structure,
The noble metal adsorbent according to any one of the above [2] to [6], wherein the half-width of the peak near 39.5° and the peak near 49.5° is 1° or more.

[8] A precious metal adsorbent described in any of [2] to [7] above, wherein the precious metal adsorbed onto the metal sulfide is gold.

[9] A method for recovering a noble metal, comprising making the noble metal adsorbent according to any one of [1] to [8] above adsorb the noble metal, and then recovering the noble metal by dissolving the noble metal adsorbent in an oxidizing solution. .

[10] After adsorbing the noble metal on the noble metal adsorbent according to any one of [1] to [8] above, recovering the noble metal by heating and volatilizing the noble metal adsorbent in the presence of oxygen. Precious metal recovery method.

[10] A method for regenerating a precious metal adsorbent, comprising recovering volatilized metal oxides by the precious metal recovery method described in [9] above, and then sulfurizing the metal oxides to regenerate a precious metal adsorbent composed of metal sulfides.

According to the present invention, it is possible to easily recover precious metals while achieving high adsorption performance for precious metals.

FIG. 1 is a schematic diagram showing an example of an apparatus used for producing molybdenum trioxide particles, which are a raw material for molybdenum disulfide particles. FIG. 2 is a diagram showing the results of the X-ray diffraction (XRD) pattern of commercially available molybdenum disulfide particles together with the diffraction pattern of the 2H crystal structure of molybdenum disulfide (MoS ₂ ). FIG. 3 is a diagram showing the X-ray diffraction (XRD) pattern results for the molybdenum disulfide particles obtained in Synthesis Example 1, together with the diffraction pattern of the 3R crystal structure of molybdenum disulfide (MoS ₂ ), the diffraction pattern of the 2H crystal structure of molybdenum disulfide (MoS ₂ ), and the diffraction pattern of molybdenum dioxide (MoO ₂ ). FIG. 4 is an AFM image of synthesized molybdenum disulfide particles. FIG. 5 is a graph showing a cross section of the molybdenum disulfide particles shown in FIG. FIG. 6 is an extended X-ray absorption fine structure (EXAFS) spectrum of the K-absorption edge of molybdenum measured using the molybdenum disulfide particles obtained in Synthesis Example 1. FIG. 7 is a diagram showing an X-ray diffraction (XRD) pattern when gold is adsorbed onto the noble metal adsorbent obtained in Synthesis Example 1 in Example 2. FIG. 8 is a diagram showing an XPS pattern when gold is adsorbed onto molybdenum disulfide particles in Example 2. FIG. 9 is a diagram showing X-ray diffraction (XRD) patterns when gold was recovered from molybdenum disulfide particles after gold adsorption in Examples 6 and 7. FIG. 10 is a graph showing the results of measuring the gold ion leakage concentration when the molybdenum disulfide particles obtained in Synthesis Example 1 were packed into a column and a gold-containing solution was passed through the column.

Below, an embodiment of the present invention is described in detail with reference to the drawings.

<Precious metal adsorbent>
The noble metal adsorbent according to this embodiment contains a metal sulfide, and is preferably composed of a metal sulfide. The noble metal adsorbent of this embodiment has selectivity to noble metals and exhibits high adsorption performance for noble metals. The metal sulfide preferably has molybdenum disulfide particles as a main component, and is more preferably composed of molybdenum disulfide particles. The high adsorption performance for noble metals is considered to be due to the fact that the median diameter _D50 of the molybdenum disulfide particles is as small as 1000 nm or less, for example. The selective adsorption performance of noble metals is considered to be due to the fact that, for example, the sulfur element in the metal sulfide exhibits a high affinity for noble metals. Examples of the form of the noble metal adsorbent include metal sulfide particles, with molybdenum disulfide particles being preferred. The metal sulfide particles preferably contain molybdenum disulfide particles, and more preferably are composed of molybdenum disulfide particles.

Examples of noble metals that can be adsorbed by the noble metal adsorbent of this embodiment include silver (Ag), gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), Examples include noble metals such as osmium (Os), and the noble metal adsorbent of this embodiment has particularly excellent adsorption performance for gold. The excellent gold adsorption performance is that the median diameter _D50 of the molybdenum disulfide particles is as small as 1000 nm or less, the 3R crystal structure of molybdenum disulfide, and/or the very high affinity between gold and sulfur. This is thought to be due to.
When using molybdenum disulfide particles as a noble metal adsorbent, the noble metals adsorbed to the molybdenum disulfide particles include gold (Au), silver (Ag), platinum (Pt), palladium (Pd), and ruthenium (Ru). One or more selected from these are preferred.

The median diameter D ₅₀ of the molybdenum disulfide particles in the noble metal adsorbent of this embodiment determined by dynamic light scattering is 10 nm or more and 1000 nm or less, and from the viewpoint of the above-mentioned effects, 600 nm or less is preferable, and 500 nm or less is more preferable. It is preferably 400 nm or less, particularly preferably 400 nm or less. The median diameter D ₅₀ of the molybdenum disulfide particles may be 10 nm or more, 20 nm or more, or 40 nm or more. The median diameter D ₅₀ of molybdenum disulfide particles can be determined using, for example, a dynamic light scattering particle size distribution analyzer (Nanotrac Wave II, manufactured by Microtrac Bell Co., Ltd.) or a laser diffraction type particle size distribution analyzer (SALD-7000, manufactured by Shimadzu Corporation). It is measured using

The molybdenum disulfide particles in the precious metal adsorbent of this embodiment preferably contain a 3R crystal structure of molybdenum disulfide. By containing the 3R crystal structure, the edge portion of the crystal of the molybdenum disulfide particles increases, and the ion adsorption sites increase, which is thought to contribute to further improvement of the adsorption performance of precious metals. In addition, by containing the 3R crystal structure, the adsorption performance of precious metals, especially gold, is significantly improved. It is presumed that this is due to the specific surface area derived from the nanostructure of the molybdenum disulfide particles.

The fact that the molybdenum disulfide particles contain a metastable 3R crystal structure can be distinguished by the fact that in the spectrum obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as the X-ray source, the peaks near 32.5°, 39.5°, and 49.5° are all composite peaks (broad peaks) of the 2H crystal structure and the 3R crystal structure.

Furthermore, it is preferable that the molybdenum disulfide particles in the noble metal adsorbent of this embodiment include a 2H crystal structure and a 3R crystal structure of molybdenum disulfide. Commercially available molybdenum disulfide particles often have a particle size exceeding 1 μm, and are hexagonal solids, with an approximately 2H crystal structure as shown in Figure 2. . On the other hand, molybdenum disulfide particles produced through the "method for producing molybdenum trioxide particles" and "method for producing molybdenum disulfide particles" described later include a 2H crystal structure and a 3R crystal structure, and have a median diameter D ₅₀ can be easily adjusted to 10 nm or more and 1000 nm or less.

The fact that molybdenum disulfide particles have a 2H crystal structure and a 3R crystal structure can be confirmed, for example, by using Rietveld analysis software (Panalytical, High Score Plus) that can take into account the crystallite size. In this Rietveld analysis software, the entire XRD diffraction profile is simulated using a crystal structure model including the crystallite size, and compared with the XRD diffraction profile obtained by experiment. The crystal lattice constants of the crystal structure model, crystal structure factors such as atomic coordinates, weight fraction (abundance ratio), etc. are optimized by the least squares method so that the residual between the diffraction profile obtained by experiment and the diffraction profile obtained by calculation is minimized, and each phase of the 2H crystal structure and the 3R crystal structure is identified and quantified with high accuracy, so that the crystallite size can be calculated in addition to the crystal structure type and its ratio calculated by normal Rietveld analysis. Hereinafter, in this patent, the analysis method using the above-mentioned High Score Plus is referred to as "extended Rietveld analysis".

Furthermore, in the profile obtained by powder X-ray diffraction (XRD) of the molybdenum disulfide particles using Cu-Kα radiation as an X-ray source, the peaks near 39.5° and near 49.5° are derived from the 2H crystal structure, and the peaks near 32.5°, 39.5°, and 49.5° are derived from the 3R crystal structure, and the half-widths of the peaks near 39.5° and 49.5° are preferably 1° or more. Furthermore, the molybdenum disulfide particles may include a crystal structure other than the 2H crystal structure and 3R crystal structure of molybdenum disulfide, such as a 1H crystal structure.

The shape of the primary particles of the molybdenum disulfide particles in a two-dimensional image taken with a transmission electron microscope (TEM) is particulate, spherical, plate-like, needle-like, string-like, ribbon-like or sheet-like. It is also possible to include a combination of these shapes. The shape of the temporary molybdenum disulfide particles is preferably a disk, a ribbon, or a sheet. Further, it is preferable that the shape of the primary particles of 50 molybdenum disulfide particles has an average size in the range of length (vertical) x width (horizontal) = 50 to 1000 nm x 50 to 1000 nm, and 100 to 500 nm. It is more preferable to have a size in the range of ×100 to 500 nm, and particularly preferably to have a size in the range of 50 to 200 nm×50 to 200 nm. Further, the shape of the primary particles of the molybdenum disulfide particles preferably has a thickness in a range of 3 nm or more, and a size in a range of 5 nm or more, as measured by an atomic force microscope (AFM). It is more preferable to have. Further, the shape of the primary particles of the molybdenum disulfide particles preferably has a thickness in a range of 100 nm or less as measured by an atomic force microscope (AFM), and a size in a range of 50 nm or less. It is more preferable to have a size of 20 nm or less. Further, the shape of the primary particles of the molybdenum disulfide particles may have a thickness in a range of 40 mm or less as measured by an atomic force microscope (AFM), and a size in a range of 30 mm or less. It may have a When the primary particles of the molybdenum disulfide particles have a disk-like, ribbon-like, or sheet-like shape, the specific surface area of the molybdenum disulfide particles can be increased. Further, it is preferable that the primary particles of the molybdenum disulfide particles have a disk-like, ribbon-like, or sheet-like shape, and have a thickness in the range of 3 to 100 nm. Here, being disk-shaped, ribbon-shaped, or sheet-shaped means that it is a thin layer shape. There is no clear distinction between disc-shaped, ribbon-shaped, and sheet-shaped, but for example, if the thickness is 10 nm or less, it is sheet-shaped, and if the thickness is 10 nm or more, and length ÷ width ≧ 2, it is ribbon-shaped, and if the thickness is 10 nm or more, it is ribbon-shaped. , if length/width<2, it can be disk-shaped. The aspect ratio of the primary particles of molybdenum disulfide particles, that is, the value of (length (length and width))/thickness (height)) is preferably 1.2 to 1200 on average of 50 particles. , more preferably from 2 to 800, even more preferably from 5 to 400, particularly preferably from 10 to 200. The shape, length, width, and thickness of the primary particles of 50 molybdenum disulfide particles can be measured by observation using an atomic force microscope (AFM), and the aspect ratio can also be calculated from the measurement results. It is possible.

Since the shape of the primary particles of the molybdenum disulfide particles is not simply spherical but is disk-shaped, ribbon-shaped or sheet-shaped with a large aspect ratio, it is expected that the contact area between the molybdenum disulfide particles and radioactive substances will be increased, which is thought to contribute to an increase in the amount of radioactive substances adsorbed.

The specific surface area of the molybdenum disulfide particles in the noble metal adsorbent of this embodiment measured by the BET method is preferably 10 m ² /g or more, more preferably 20 m ² /g or more, and particularly preferably 30 m ² /g or more. The specific surface area of the molybdenum disulfide particles measured by the BET method may be 40 m ² /g or more, 50 m ² /g or more, or 60 m ² /g or more. The specific surface area of the molybdenum disulfide particles measured by the BET method may be 300 m ² /g or less, 200 m ² /g or less, or 100 m ² /g or less.

In the precious metal adsorbent of this embodiment, the molybdenum disulfide particles have a specific surface area of 10 ^m2 /g or more as measured by the BET method, and therefore the contact area with the precious metal can be increased, which is believed to improve the adsorption performance of the precious metal.

In the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the molybdenum K absorption edge of the molybdenum disulfide particles in the noble metal adsorbent of this embodiment, the intensity I of the peak due to Mo-S and The ratio (I/II) to the peak intensity II due to Mo-Mo is preferably larger than 1.0, more preferably 1.1 or more, particularly preferably 1.2 or more.

Whether the crystal structure of molybdenum disulfide is a 2H crystal structure or a 3R crystal structure, the distance between Mo-S is approximately the same due to a covalent bond, and therefore the intensity of the peak due to Mo-S is the same in the extended X-ray absorption fine structure (EXAFS) spectrum at the K absorption edge of molybdenum. On the other hand, since the 2H crystal structure of molybdenum disulfide is hexagonal, the same hexagon is located 90° directly below the hexagon of Mo atoms, so the distance between Mo-Mo is closer and the peak intensity II due to Mo-Mo is stronger.
Conversely, since the 3R crystal structure of molybdenum disulfide is rhombohedral, the hexagon is not directly below the hexagon by 90° but is shifted by half, which increases the distance between Mo-Mo and weakens the peak intensity II due to Mo-Mo.
In the pure 2H crystal structure of molybdenum disulfide, the ratio (I/II) is small, but as the 3R crystal structure is included, the ratio (I/II) becomes large.
In the 3R crystal structure, the hexagons of the Mo atoms in each of the three layers are offset from each other by half a hexagon. This means that the interactions between the layers are smaller than in the 2H crystal structure, in which the hexagons of the Mo atoms in two layers are regularly aligned perpendicular to each other. This is expected to make it easier for precious metals to be adsorbed.

The conversion rate R _C of molybdenum disulfide particles to MoS ₂ in the noble metal adsorbent of this embodiment is preferably 70% or more, and 80% or more, since the presence of molybdenum trioxide is considered to have a negative effect on the noble metal adsorption performance. % or more, and particularly preferably 90% or more.
The molybdenum disulfide particles in the noble metal adsorbent of this embodiment can exhibit a conversion rate R _C to MoS ₂ of nearly 100%, making it possible to use other molybdenum disulfide materials that can produce or contain molybdenum trioxide as a by-product. The noble metal adsorption performance can be made superior to that of the precursor.

The conversion rate R _C of the molybdenum disulfide particles to MoS ₂ in the precious metal adsorbent of this embodiment can be obtained from profile data obtained by subjecting the molybdenum disulfide particles to X-ray diffraction (XRD) measurement, using the RIR (reference intensity ratio) method described later.

The radioactive substance adsorbent of this embodiment is preferably composed of molybdenum disulfide particles (MoS ₂ ), but is not limited to this, and may be composed of molybdenum sulfide particles represented by MoS _x (X = 1 to 3). or one or more types of molybdenum sulfide particles represented by MoS _x (X=1 to 3).

The noble metal adsorbent of this embodiment can adsorb and remove or recover noble metal ions, noble metals, or noble metal compounds contained in a noble metal-containing solution, for example, a noble metal-containing aqueous solution. Moreover, the noble metal adsorbent of this embodiment can adsorb and remove or recover the noble metal or noble metal compound contained in the noble metal-containing gas.

When the precious metal adsorbent of this embodiment is used, the precious metal can be recovered from a solution with an extremely low initial concentration of the precious metal. For example, the initial concentration of the precious metal in the precious metal solution to be treated can be 10 ppm or less, 1 ppm or less, or 100 ppb or less. In particular, when the metal is gold, the initial concentration can be 10 ppb or less, or 5 ppb or less.

<Method for producing noble metal adsorbent>
The method for producing the noble metal adsorbent according to the present embodiment is not particularly limited, but can be produced, for example, by heating a metal oxide in the presence of a sulfur source. Further, the noble metal adsorbent of this embodiment is not limited to that obtained by the above manufacturing method, and may be a commercially available metal sulfide, such as commercially available molybdenum disulfide particles, as long as it can exhibit the adsorption performance of the present invention. .

(Method for producing molybdenum disulfide particles in precious metal adsorbent)
The molybdenum disulfide particles in the noble metal adsorbent of this embodiment can be produced, for example, by heating molybdenum trioxide particles at a temperature of 200 to 1000° C. in the presence of a sulfur source.

The average particle diameter of the primary particles of the molybdenum trioxide particles is preferably 2 nm or more and 1000 nm or less. The average particle diameter of the primary particles of molybdenum trioxide particles is the smallest particle size that constitutes an aggregate on a two-dimensional image of molybdenum trioxide particles photographed with a scanning electron microscope (SEM) or transmission electron microscope (TEM). For a unit particle (i.e., primary particle), measure its major axis (the Feret diameter of the longest observed part) and the minor axis (the short Feret diameter perpendicular to the Feret diameter of the longest part). , the average value is the primary particle diameter of 50 randomly selected primary particles.

In the method for producing molybdenum disulfide particles of this embodiment, the average particle size of the primary particles of the molybdenum trioxide particles is preferably 1 μm or less. From the viewpoint of reactivity with sulfur, it is more preferable that it is 600 nm or less, even more preferable that it is 400 nm or less, and particularly preferable that it is 200 nm or less. The average particle size of the primary particles of the molybdenum trioxide particles may be 2 nm or more, 5 nm or more, or 10 nm or more.

The molybdenum trioxide particles used in the production of the molybdenum disulfide particles in the noble metal adsorbent of this embodiment are preferably composed of an aggregate of primary particles containing a β crystal structure of molybdenum trioxide. The molybdenum trioxide particles have a better reactivity with sulfur than conventional molybdenum trioxide particles that are composed only of α crystals as a crystal structure, and since they contain the β crystal structure of molybdenum trioxide, they can increase the conversion rate R _C to _MoS2 in the reaction with a sulfur source.

The β-crystal structure of molybdenum trioxide can be confirmed by the presence of a peak (2θ: around 23.01°, No. 86426 (Inorganic Crystal Structure Database, ICSD)) that belongs to the (011) plane of the β-crystal of _MoO3 in a spectrum obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source. The α-crystal structure of molybdenum trioxide can be confirmed by the presence of a peak (2θ: around 27.32°, No. 166363 (Inorganic Crystal Structure Database, ICSD)) that belongs to the (021) plane of the α-crystal of _MoO3 .

In the profile obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source, the molybdenum trioxide particles preferably have a peak intensity attributable to the (011) plane of the β crystal of _MoO3 (2θ: approximately 23.01°, No. 86426 (Inorganic Crystal Structure Database (ICSD))) to a peak intensity attributable to the (021) plane of the α crystal of _MoO3 (2θ: approximately 27.32°, No. 166363 (Inorganic Crystal Structure Database (ICSD))) having a ratio (β(011)/α(021)) of 0.1 or more.

For the peak intensity attributable to the (011) plane of the β crystal of _MoO3 and the peak intensity attributable to the (021) plane of the α crystal of _MoO3 , the maximum intensity of the peak is read, and the ratio (β(011)/α(021)) is calculated.

In the molybdenum trioxide particles, the ratio (β(011)/α(021)) is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and 0. A range of .4 to 10.0 is particularly preferred.

The β-crystalline structure of molybdenum trioxide can also be confirmed by the presence of peaks at wave numbers of 773, 848 cm ⁻¹ and 905 cm ⁻¹ in the Raman spectrum obtained from Raman spectroscopy. The α-crystalline structure of molybdenum trioxide can be confirmed by the presence of peaks at wave numbers of 663, 816 cm ⁻¹ and 991 cm ⁻¹ .

In the manufacturing method of this embodiment, the average particle size of the primary particles of the molybdenum trioxide particles may be 5 nm or more and 2000 nm or less.

Examples of sulfur sources include sulfur, hydrogen sulfide, etc., which may be used alone or in combination.

In the manufacturing method of the present embodiment, molybdenum trioxide particles consisting of an aggregate of primary particles containing a β crystal structure of molybdenum trioxide are heated at a temperature of 100 to 800°C in the absence of a sulfur source, and then the sulfur source It may include heating at a temperature of 200 to 1000°C in the presence of.

The heating time in the presence of a sulfur source may be a time sufficient for the sulfurization reaction to proceed sufficiently, and may be 1 to 20 hours, 2 to 15 hours, or 3 to 10 hours.

In the method for producing molybdenum disulfide particles of this embodiment, the ratio of the amount of _S in the sulfur source to the amount of _MoO3 in the molybdenum trioxide particles is preferably set under conditions in which the sulfurization reaction proceeds sufficiently. The amount of S in the sulfur source is preferably 450 mol% or more, preferably 600 mol% or more, and preferably 700 mol% or more, relative to 100 mol% of the amount of MoO3 in the molybdenum trioxide particles. The amount of S in the sulfur source may be 3000 mol% or less, 2000 mol% or less, or 1500 mol% or less, relative to 100 mol% of the amount of _MoO3 in the molybdenum trioxide particles.

In the production method of this embodiment, the heating temperature in the presence of the sulfur source may be any temperature at which the sulfidation reaction sufficiently proceeds, and is preferably 320°C or higher, more preferably 340°C or higher. , 360°C or higher is particularly preferred. The temperature may be 320 to 1000°C, 340 to 800°C, or 360 to 600°C.
The heating temperature in the presence of the sulfur source is in the range of 320 to 1000°C, and molybdenum disulfide particles with higher crystallinity can be synthesized as the temperature is higher. Moreover, the heating temperature in the presence of the sulfur source is in the temperature range of 320 to 1000° C., and the lower the heating temperature, the higher the specific surface area of molybdenum disulfide particles can be synthesized.

In the method for producing molybdenum disulfide particles of the present embodiment, it is preferable that the molybdenum trioxide particles have a MoO ₃ content of 99.5% or more as measured by X-ray fluorescence (XRF), and thereby, The conversion rate R _C to MoS ₂ can be increased, and molybdenum disulfide with high purity and good storage stability can be obtained without the risk of generating sulfides derived from impurities.

The molybdenum trioxide particles preferably have a specific surface area, as measured by the BET method, of 10 m ² /g or more and 100 m ² /g or less.

In the molybdenum trioxide particles, the specific surface area is preferably 10 m ² /g or more, preferably 20 m ² /g or more, and 30 m ² /g because the reactivity with sulfur becomes good. It is preferable that it is above. In the molybdenum trioxide particles, the particle size is preferably 100 m ² /g or less, may be 90 m ² /g or less, or may be 80 m ² /g or less, since manufacturing becomes easy.

The molybdenum trioxide particles have an intensity I of a peak due to Mo-O and a peak due to Mo-Mo in a radial distribution function obtained from an extended X-ray absorption fine structure (EXAFS) spectrum at the K absorption edge of molybdenum. It is preferable that the ratio (I/II) to intensity II is greater than 1.1.

For the peak intensity I due to Mo-O and the peak intensity II due to Mo-Mo, the maximum intensity of each peak is read and the ratio (I/II) is determined. The ratio (I/II) is considered to be an indicator that the β crystal structure of MoO ₃ is obtained in the molybdenum trioxide particles, and the larger the ratio (I/II), the greater the reactivity with sulfur. Excellent in

In the molybdenum trioxide particles, the ratio (I/II) is preferably 1.1 to 5.0, may be 1.2 to 4.0, or may be 1.2 to 3.0.

(Method for producing molybdenum trioxide particles)
The molybdenum trioxide particles can be produced by vaporizing a molybdenum trioxide precursor compound to form molybdenum trioxide vapor and cooling the molybdenum trioxide vapor.

The method for producing the molybdenum trioxide particles includes calcining a raw material mixture containing a molybdenum trioxide precursor compound and a metal compound other than the molybdenum trioxide precursor compound, and vaporizing the molybdenum trioxide precursor compound to form molybdenum trioxide vapor, and it is preferable that the proportion of the metal compound relative to 100% by mass of the raw material mixture is 70% by mass or less in terms of oxide.

The method for producing molybdenum trioxide particles can be suitably carried out using a production apparatus 1 shown in FIG.

FIG. 1 is a schematic diagram of an example of an apparatus used for producing the molybdenum trioxide particles. The manufacturing apparatus 1 is connected to a firing furnace 2 for firing a molybdenum trioxide precursor compound or the raw material mixture and vaporizing the molybdenum trioxide precursor compound, and a firing furnace 2 for firing a molybdenum trioxide precursor compound or the raw material mixture and for vaporizing the molybdenum trioxide precursor compound. It has a cross-shaped cooling pipe 3 that converts molybdenum oxide vapor into particles, and a recovery machine 4 that is a recovery means for recovering molybdenum trioxide particles formed into particles in the cooling pipe 3. At this time, the firing furnace 2 and the cooling pipe 3 are connected via the exhaust port 5. Further, the cooling pipe 3 has an opening adjustment damper 6 disposed at an outside air intake port (not shown) at the left end thereof, and an observation window 7 at the upper end thereof. A ventilation device 8, which is a first ventilation means, is connected to the recovery machine 4. When the air exhaust device 8 exhausts air, the recovery machine 4 and the cooling pipe 3 are sucked, and outside air is blown into the cooling pipe 3 from the opening adjustment damper 6 that the cooling pipe 3 has. That is, when the air exhaust device 8 performs a suction function, air is passively blown into the cooling pipe 3. Note that the manufacturing apparatus 1 may include an external cooling device 9, thereby making it possible to arbitrarily control the cooling conditions of the molybdenum trioxide vapor generated from the firing furnace 2.

The opening adjustment damper 6 takes in air from the outside air intake port, and the molybdenum trioxide vapor vaporized in the firing furnace 2 is cooled in an air atmosphere to form molybdenum trioxide particles, thereby achieving the ratio (I/II). can be made larger than 1.1, and the β crystal structure of MoO ₃ is easily obtained in the molybdenum trioxide particles. Cooling molybdenum trioxide vapor in a state where the oxygen concentration is low in a nitrogen atmosphere, such as when molybdenum trioxide vapor is cooled using liquid nitrogen, increases the oxygen defect density and lowers the ratio (I/II). Easy to lower.

There are no particular limitations on the molybdenum trioxide precursor compound, so long as it is a precursor compound for forming molybdenum trioxide particles consisting of an aggregate of primary particles containing the β crystal structure of molybdenum trioxide.

The molybdenum trioxide precursor compound is not particularly limited as long as it forms molybdenum trioxide vapor when fired, but metal molybdenum, molybdenum trioxide, molybdenum dioxide, molybdenum disulfide, ammonium molybdate, and phosphomolybdenum can be used. Acid (H ₃ PMo ₁₂ O ₄₀ ), silicomolybdic acid (H ₄ SiMo ₁₂ O ₄₀ ), aluminum molybdate, silicon molybdate, magnesium molybdate (MgMo _n O _3n+1 (n=1-3)), sodium molybdate (Na _{2 Mon} O _3n+1 (n=1-3)), titanium molybdate, iron molybdate, potassium molybdate (K _{2 Mon} O _3n+1 (n=1-3)), zinc molybdate, boron molybdate , lithium molybdate (Li _{2 Mon} O _3n+1 (n=1-3)), cobalt molybdate, nickel molybdate, manganese molybdate, chromium molybdate, cesium molybdate, barium molybdate, strontium molybdate, molybdate Examples include yttrium, zirconium molybdate, copper molybdate, and the like. These molybdenum trioxide precursor compounds may be used alone or in combination of two or more. The form of the molybdenum trioxide precursor compound is not particularly limited, and may be, for example, in the form of a powder such as molybdenum trioxide, or in the form of a liquid such as an aqueous ammonium molybdate solution. Preferably, it is in powder form, which is easy to handle and has good energy efficiency.

It is preferable to use commercially available α-crystalline molybdenum trioxide as the molybdenum trioxide precursor compound. When ammonium molybdate is used as the molybdenum oxide precursor compound, it is converted to thermodynamically stable molybdenum trioxide by calcination, and the vaporized molybdenum oxide precursor compound becomes the molybdenum trioxide.

Molybdenum trioxide vapor can also be formed by calcining a raw material mixture containing a molybdenum trioxide precursor compound and a metal compound other than the molybdenum trioxide precursor compound.

Among these, the molybdenum oxide precursor compound preferably contains molybdenum trioxide in terms of ease of controlling the purity, average particle size of primary particles, and crystal structure of the molybdenum trioxide particles obtained.

A molybdenum trioxide precursor compound and a metal compound other than the molybdenum trioxide precursor compound may form an intermediate, but even in this case, the intermediate is decomposed by calcination, and molybdenum trioxide is thermodynamically It can be vaporized in a stable form.

When firing a raw material mixture containing a molybdenum trioxide precursor compound and a metal compound other than the molybdenum trioxide precursor compound, the content ratio of the molybdenum trioxide precursor compound is 40% by mass with respect to 100% by mass of the raw material mixture. It is preferably from 100% by weight, may be from 45 to 100% by weight, and may be from 50 to 100% by weight.

The firing temperature varies depending on the molybdenum trioxide precursor compound, metal compound, and desired molybdenum trioxide particles used, but is usually preferably set to a temperature at which the intermediate can be decomposed. For example, when a molybdenum compound is used as the molybdenum trioxide precursor compound and an aluminum compound is used as the metal compound, aluminum molybdate may be formed as an intermediate, so the firing temperature is preferably 500 to 1500°C, more preferably 600 to 1550°C, and even more preferably 700 to 1600°C.

There is no particular restriction on the firing time, and it can be, for example, 1 min to 30 h, 10 min to 25 h, or 100 min to 20 h.

The temperature increase rate varies depending on the molybdenum trioxide precursor compound used, the metal compound, and the desired characteristics of the molybdenum trioxide particles, but from the viewpoint of production efficiency, it is 0.1°C/min or more and 100°C/min. It is preferably at most 1°C/min and at most 50°C/min, and even more preferably at least 2°C/min and at most 10°C/min.

Next, the molybdenum trioxide vapor is cooled and turned into particles.
Molybdenum trioxide vapor is cooled by lowering the temperature of the cooling piping. At this time, examples of the cooling means include cooling by blowing gas into the cooling pipe, cooling by a cooling mechanism included in the cooling pipe, cooling by an external cooling device, etc. as described above.

The molybdenum trioxide vapor is preferably cooled under an air atmosphere. By cooling molybdenum trioxide vapor in an air atmosphere to form molybdenum trioxide particles, the ratio (I/II) can be made larger than 1.1, and in the molybdenum trioxide particles, β crystals of MoO ₃ Structure is easy to obtain.

The cooling temperature (temperature of the cooling pipe) is not particularly limited, but is preferably -100 to 600°C, and more preferably -50 to 400°C.

The cooling rate of molybdenum trioxide vapor is not particularly limited, but is preferably 100°C/s or more and 100,000°C/s or less, more preferably 1000°C/s or more and 50,000°C/s or less. Note that the faster the cooling rate of the molybdenum trioxide vapor, the more molybdenum trioxide particles tend to be obtained with a smaller particle size and a larger specific surface area.

When the cooling means is cooling by blowing gas into the cooling pipe, the temperature of the gas blown is preferably -100 to 300°C, and more preferably -50 to 100°C.

The particles obtained by cooling the molybdenum trioxide vapor are transported to a recovery machine and recovered.

The method for producing the molybdenum trioxide particles may involve cooling the molybdenum trioxide vapor and then calcining the resulting particles again at a temperature of 100 to 320°C.

That is, the molybdenum trioxide particles obtained by the method for producing molybdenum trioxide particles may be fired again at a temperature of 100 to 320°C. The firing temperature for the second firing may be 120 to 280°C, or 140 to 240°C. The firing time for the second firing can be, for example, 1 min to 4 h, 10 min to 5 h, or 100 min to 6 h. However, by firing again, a part of the β crystal structure of molybdenum trioxide disappears, and when fired at a temperature of 350°C or higher for 4 hours, the β crystal structure in the molybdenum trioxide particles disappears. , the ratio (β(011)/α(021)) becomes 0, and the reactivity with sulfur is impaired.

By the method for producing a precious metal adsorbent, the molybdenum disulfide particles in the precious metal adsorbent of this embodiment can be produced.
Moreover, by the method for producing molybdenum trioxide particles, it is possible to produce molybdenum trioxide particles suitable for producing molybdenum disulfide particles in the noble metal adsorbent of this embodiment.

<Precious metal recovery method>
In the precious metal recovery method according to the present embodiment, after the precious metal is adsorbed by the precious metal adsorbent, the precious metal adsorbent is dissolved in an oxidizing solution to recover the precious metal. In addition, in the precious metal recovery method according to the present embodiment, after the precious metal is adsorbed by the precious metal adsorbent, the precious metal adsorbent is heated in the presence of oxygen to volatilize the precious metal, thereby recovering the precious metal.

By removing the precious metal adsorbent with acid or heat while the precious metal is adsorbed on the precious metal adsorbent, the precious metal can be easily recovered through a simple process. Furthermore, when molybdenum disulfide particles are used as the precious metal adsorbent, the precious metal, particularly gold, is reduced to a valence of zero, making reduction treatment of the precious metal element unnecessary, and it becomes possible to easily recover high-purity gold simply by removing the molybdenum disulfide particles, and also eliminating the environmental burden associated with reduction treatment.

When the precious metal adsorbent is dissolved in an oxidizing solution, the oxidizing solution may be, for example, nitric acid or hydrogen peroxide.

When the molybdenum disulfide particles as the precious metal adsorbent are heated in the presence of oxygen, the heating temperature is preferably 400 to 1500°C, more preferably 650 to 1200°C, and even more preferably 750 to 950°C. When the molybdenum disulfide particles are heated in the presence of oxygen, the molybdenum disulfide is oxidized to molybdenum trioxide, which vaporizes at a relatively low heating temperature due to the high volatility of molybdenum trioxide. For this reason, the precious metal and the molybdenum disulfide particles can be easily separated, and the precious metal can be easily recovered. From the viewpoint of energy efficiency, a low temperature is preferable, but a temperature at which the volatilization rate of molybdenum trioxide is sufficient is preferable. 400°C is the temperature at which molybdenum disulfide is oxidized, and molybdenum trioxide volatilizes smoothly at 750°C or higher.

<Regeneration method of precious metal adsorbent>
The method for regenerating a noble metal adsorbent of the present embodiment includes recovering the metal oxide volatilized by the above-described precious metal recovery method and then sulfurizing the metal oxide to regenerate the noble metal adsorbent composed of the metal sulfide. .

In this regeneration method, the metal oxide vapor obtained by the above precious metal recovery method may be sulfurized as it is, or it may be cooled once to form metal oxide particles, and then the metal oxide particles may be sulfurized in the presence of a sulfur source. The metal oxide particles may be sulfurized by heating the metal oxide.

When molybdenum disulfide particles are used as the precious metal adsorbent, the molybdenum trioxide volatilized by the above-mentioned precious metal recovery method can be recovered, and the recovered molybdenum trioxide particles can then be sulfurized, for example, by a method similar to the above-mentioned method for producing molybdenum disulfide particles. This makes it possible to easily regenerate the molybdenum disulfide particles as a precious metal adsorbent, and by reusing the obtained molybdenum disulfide particles as a precious metal adsorbent, consumption of molybdenum resources can be suppressed.

The present invention will now be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

[Method for measuring the average particle diameter of primary particles of molybdenum trioxide particles]
Molybdenum trioxide particles constituting the molybdenum trioxide particles were photographed using a scanning electron microscope (SEM). Regarding the smallest unit particle (i.e., primary particle) constituting the aggregate on the two-dimensional image, its major axis (the Feret diameter of the longest part observed) and the minor axis (with respect to the Feret diameter of the longest part), The short Feret diameter in the vertical direction was measured, and the average value was taken as the primary particle diameter. The same operation was performed on 50 randomly selected primary particles, and the average particle size of the primary particles was calculated from the average value of the primary particle size of the primary particles.

[Purity measurement of molybdenum trioxide: XRF analysis]
Using a fluorescent X-ray analyzer (Primus IV, manufactured by Rigaku Corporation), about 70 mg of a sample of the recovered molybdenum trioxide particles was placed on a filter paper, covered with a PP film, and the composition was analyzed. The amount of molybdenum determined from the XRF analysis results was determined in terms of molybdenum trioxide (% by mass) based on 100% by mass of molybdenum trioxide particles.

[Crystal structure analysis: XRD method]
The collected molybdenum trioxide particles or a sample of its sulfide were filled into a measurement sample holder having a depth of 0.5 mm, which was then set in a wide-angle X-ray diffraction (XRD) device (Ultima IV, manufactured by Rigaku Corporation) and measured under the conditions of Cu/Kα radiation, 40 kV/40 mA, a scan speed of 2°/min, and a scan range of 10° to 70°.

[Specific surface area measurement: BET method]
A sample of molybdenum trioxide particles or molybdenum disulfide particles is measured using a specific surface area meter (BELSORP-mini, manufactured by Microtrack Bell Co., Ltd.), and the surface area per gram of the sample is determined from the amount of nitrogen gas adsorbed by the BET method. , was calculated as specific surface area (m ² /g).

[Conversion rate R _C to MoS ₂ ]
According to the RIR (Reference Intensity Ratio) method, the RIR value _KA of molybdenum disulfide (MoS ₂ ) and the (002) or (003) plane of molybdenum disulfide (MoS ₂ ), 2θ = 14.4° The integrated intensity I _A of the peak around ±0.5° and the RIR value K of each molybdenum oxide (raw material MoO ₃ and reaction intermediates Mo ₉ O ₂₅ , Mo ₄ O ₁₁ , MoO ₂ , etc.) Using the integrated intensity I _B of the strongest line peak of _B and each molybdenum oxide (raw material MoO ₃ and reaction intermediates Mo ₉ O ₂₅ , Mo ₄ O ₁₁ , MoO ₂ , etc.), the following formula (1 ) to MoS ₂ was _determined .
R _C (%)=(I _A /K _A )/(Σ(I _B /K _B ))×100...(1)
Here, the values listed in the Inorganic Crystal Structure Database (ICSD) were used as the RIR values, and the integrated powder X-ray analysis software (PDXL) (manufactured by Rigaku Corporation) was used for the analysis.

[Extensive X-ray absorption fine structure (EXAFS) measurement]
36.45 mg of molybdenum disulfide powder and 333.0 mg of boron nitride (manufactured by Kishida Chemical Co., Ltd.) were mixed in a mortar. 123.15 mg of this mixture was weighed out and compressed into a tablet with a diameter of 8 mm to obtain a measurement sample. Using this measurement sample, the wide-area X-ray absorption fine structure (EXAFS) was measured using the transmission method at BL5S1 at the Aichi Synchrotron Optical Center. Athena (Internet <URL: https://bruceravel.github.io/demeter/>) was used for the analysis.

[Measurement of median diameter _D50 of molybdenum disulfide particles]
0.1 g of molybdenum disulfide powder was added to 20 cc of acetone, and ultrasonicated in an ice bath for 4 hours, after which the concentration was appropriately adjusted with acetone to a range measurable by a dynamic light scattering particle size distribution measuring device (Microtrackbell, Nanotrac WaveII) to obtain a measurement sample. Using this measurement sample, the particle size distribution in the particle size range of 0.0001 to 10 μm was measured by the dynamic light scattering particle size distribution measuring device, and the median diameter _D50 was calculated.
However, for those with a median diameter _D50 exceeding 10 μm, a solution was prepared in the same manner, and the particle size distribution in the particle size range of 0.015 to 500 μm was measured using a laser diffraction particle size distribution measuring device (Shimadzu Corporation, SALD-7000), and the median diameter _D50 was calculated.

[Method for observing particle shape of molybdenum disulfide particles]
The molybdenum disulfide particles were measured using an atomic force microscope (AFM) (Oxford Cypher-ES), and the particle shape was observed.

(Commercially available molybdenum trioxide particles)
The results of the X-ray diffraction (XRD) pattern of a commercially available molybdenum disulfide reagent (manufactured by Kanto Kagaku Co., Ltd.) are shown in FIG. 2 together with the diffraction pattern of molybdenum disulfide having a 2H crystal structure. This commercially available molybdenum disulfide reagent was found to be molybdenum disulfide with a 2H crystal structure of 99% or more. The half widths of the peak near 39.5° and the peak near 49.5° were 0.23° and 0.22°, respectively.

Regarding commercially available molybdenum disulfide particles, the specific surface area (SA), the intensity I of the peak due to Mo-S obtained from the measurement of the extended X-ray absorption fine structure (EXAFS) of the K absorption edge of molybdenum, and the Mo-Mo The ratio (I/II) to the resulting peak intensity II was 1.2.
The specific surface area of commercially available molybdenum disulfide particles was measured by the BET method and was found to be 5.6 m ² /g.
Further, the particle size distribution of commercially available molybdenum disulfide particles was measured using a dynamic light scattering particle size distribution measuring device, and the median diameter _D50 was determined to be 13,340 nm.

(Synthesis Example 1)
(Production of Molybdenum Trioxide Particles)
1 kg of transition aluminum oxide (Wako Pure Chemical Industries, Ltd., activated alumina, average particle size 45 μm) and 1 kg of molybdenum trioxide (Taiyo Koko Co., Ltd.) were mixed and then charged into a sagger, and calcined for 10 hours at a temperature of 1100° C. in the calcination furnace 2 of the manufacturing apparatus 1 shown in FIG. 1. During the calcination, outside air (air flow rate: 50 L/min, outside air temperature: 25° C.) was introduced from the side and bottom of the calcination furnace 2. After evaporating in the calcination furnace 2, the molybdenum trioxide was cooled near the recovery machine 4 and precipitated as particles. An RHK simulator (Noritake Co., Ltd.) was used as the calcination furnace 2, and a VF-5N dust collector (Amano Co., Ltd.) was used as the recovery machine 4.

After firing, 1.0 kg of blue particles of aluminum oxide and 0.85 kg of molybdenum trioxide particles recovered by the recovery machine 4 were taken out from the pod. The recovered molybdenum trioxide particles had an average primary particle diameter of 80 nm, and X-ray fluorescence (XRF) measurement confirmed that the purity of the molybdenum trioxide was 99.7%. The specific surface area (SA) of the molybdenum trioxide particles measured by the BET method was 44.0 m ² /g.

(Production of Molybdenum Disulfide Particles)
In a magnetic crucible, 1.00 g of molybdenum trioxide particles and 1.57 g of sulfur powder (manufactured by Kanto Chemical Co., Ltd.) were mixed with a stirring rod so that the powder was uniform, and then calcined at 500° C. for 4 hours in a nitrogen atmosphere to obtain a black powder. Here, the amount of S in the sulfur was 705 mol % relative to the amount of MoO ₃ in the molybdenum trioxide particles of 100 mol %. The results of the X-ray diffraction (XRD) pattern of this black powder (molybdenum disulfide particles of Synthesis Example 1) are shown in FIG. 3 together with the diffraction pattern of the 3R crystal structure of molybdenum disulfide (MoS ₂ ), the diffraction pattern of the 2H crystal structure of molybdenum disulfide (MoS ₂ ), and the diffraction pattern of molybdenum dioxide (MoO ₂ ) described in the Inorganic Crystal Structure Database (ICSD). Molybdenum dioxide (MoO ₂ ) is a reaction intermediate.

In the X-ray diffraction (XRD) pattern of Fig. 3, only peaks attributable to molybdenum disulfide ( _MoS2 ) were detected, and no peaks not attributable to molybdenum disulfide ( _MoS2 ) were observed. In other words, no peaks of reaction intermediates such as by-product molybdenum dioxide ( _MoO2 ) were observed, and only peaks attributable to molybdenum disulfide ( _MoS2 ) were observed. This confirmed that the molybdenum disulfide particles of Synthesis Example 1 had a conversion rate of 99% or more to _MoS2 , and that the reaction with sulfur proceeded quickly.
The crystal structure of the molybdenum disulfide particles of Synthesis Example 1 was analyzed by X-ray diffraction (XRD), and it was confirmed that the particles contained a 2H crystal structure and a 3R crystal structure. The half-widths of the peaks near 39.5° and 49.5° were 2.36° and 3.71°, respectively, which were wider than those of commercially available molybdenum trioxide particles.

The specific surface area of the molybdenum disulfide particles of Synthesis Example 1 was measured by the BET method and was found to be 67.8 m ² /g.

The particle size distribution of the molybdenum disulfide particles of Synthesis Example 1 was measured using a dynamic light scattering particle size distribution measuring device, and the median diameter _D50 was determined to be 170 nm.

FIG. 4 shows an AFM image of the synthesized molybdenum disulfide particles. FIG. 4 is an AFM image obtained by measurement, showing the upper surface of the molybdenum disulfide particles. When the length (vertical) x width (horizontal) was determined from this AFM image, it was found to be 180 nm x 80 nm. FIG. 5 is a graph showing a cross section of the molybdenum disulfide particles shown in FIG. The thickness (height) was determined from this cross-sectional view and was 16 nm. Therefore, the value of the aspect ratio (length (vertical)/thickness (height)) of the primary particles of molybdenum disulfide particles was 11.25.

The average value of 50 molybdenum disulfide particles including the molybdenum disulfide particles shown in FIG. 4 was length (length) x width (horizontal) x thickness (height) = 198 nm x 158 nm x 19 nm.

Table 1 shows representative examples of AFM measurement results of molybdenum disulfide particles. In the table, "molybdenum disulfide particles (1)" are the molybdenum disulfide particles shown in FIG. 3. "Molybdenum disulfide particles (2)" are the longest particles among the measured molybdenum disulfide particles, and "molybdenum disulfide particles (3)" are the shortest particles. "Molybdenum disulfide particles (4)" are relatively thick particles, and "molybdenum disulfide particles (5)" are the thinnest particles. "Molybdenum disulfide particles (6)" are particles with the largest aspect ratio. "Molybdenum disulfide particles (7)" are the thickest particles and the particles with the smallest aspect ratio.

The extended X-ray absorption fine structure (EXAFS) of the molybdenum disulfide particles of Synthesis Example 1 was measured. Figure 4 shows the extended X-ray absorption fine structure (EXAFS) spectrum of the K-edge of molybdenum. In the radial distribution function obtained from this spectrum, the ratio (I/II) between the peak intensity I due to Mo-S and the peak intensity II due to Mo-Mo was 1.2.

(Synthesis Example 2)
Molybdenum disulfide particles were produced in the same manner and under the same conditions as in Synthesis Example 1, except that the firing temperature was changed to 400°C.

The specific surface area of the molybdenum disulfide particles of Synthesis Example 2 was measured by the BET method and was found to be 80.4 m ² /g.

The particle size distribution of the molybdenum disulfide particles of Synthesis Example 2 was measured by a dynamic light scattering particle size distribution measuring device, and the median diameter _D50 was calculated to be 270 nm.

[Precious metal (gold) adsorption evaluation]
<Example 1>
A 1000 ppm gold standard solution (manufactured by Nacalai Tesque) was diluted with ion-exchanged water to prepare a diluted solution with an initial gold concentration of 561 ppm.
30 g of the obtained diluted solution was put into a 50 mL polyester test tube, 30 mg of commercially available molybdenum disulfide powder (manufactured by Kanto Kagaku Co., Ltd., Molybdenum Disulfide Reagent) was added as an adsorbent, and an overturning rotary stirrer (manufactured by Towarabo Co., Ltd.) was added. , Rotor Mix RKVSD) at a rotation speed of 15 rpm for 24 hours.
After each stirring time of 3 hours, 6 hours, and 24 hours has elapsed, filtration is performed using a 0.2 μm syringe filter, and the remaining gold concentration in the sample solution is measured using an ICP optical emission spectrometer (ICP-OES, manufactured by PerkinElmer). , Optima 8300). Further, using the residual gold concentration in the sample solution after 24 hours and the input amount of molybdenum disulfide powder, the amount of gold adsorbed per gram of adsorbent in 24 hours (g/g) was calculated from the following formula.
24-hour gold adsorption amount = (initial gold concentration - gold concentration after 24 hours) x liquid volume / amount of molybdenum disulfide powder input

Example 2
The remaining gold concentration in the sample solution after 24 hours and the amount of gold adsorbed per gram of adsorbent (g/g) after 24 hours were calculated in the same manner as in Example 1, except that the molybdenum disulfide powder obtained in Synthesis Example 1 was used instead of the commercially available molybdenum disulfide powder.

<Example 3>
The procedure was the same as in Example 1 except that 10 mg of the molybdenum disulfide powder of Synthesis Example 1 was added to 50 g of the diluted solution with an initial gold concentration of 470 ppm, and the remaining gold concentration in the sample solution after 24 hours and per 1 g of adsorbent were The amount of gold adsorbed in 24 hours was calculated.

<Example 4>
The procedure was the same as in Example 3 except that the amount of molybdenum disulfide powder in Synthesis Example 1 was changed to 5 mg. The amount of gold adsorbed was calculated.

<Comparative Example 1>
The amount of gold adsorbed per gram of adsorbent in 24 hours was calculated in the same manner as in Example 1, except that carbon (Kuraray Co., Ltd., Kuraray Coal (registered trademark)) was used instead of the commercially available molybdenum disulfide powder.

From the results in Table 2, in Example 1, when 30 mg of commercially available molybdenum disulfide powder was used as an adsorbent, the gold concentration in the solution after 24 hours was 555 ppm, and the amount of gold adsorbed was 0.006 (g/g). Met.

In Example 2, when 30 mg of the molybdenum disulfide powder of Synthesis Example 1 was used, the gold concentration in the solution after 24 hours was less than 0.1 ppm, and the amount of gold adsorption was 0.56 (g/g). This shows that the gold adsorption performance is significantly higher than that of the commercially available molybdenum disulfide particles of Example 1.
In Example 2, the molybdenum disulfide powder after gold adsorption was subjected to XRD measurement. As shown in FIG. 5, from the diffraction pattern of the molybdenum disulfide powder (Synthesis Example 1) before gold adsorption and the spectral peak of gold (zero valence), it was confirmed that the molybdenum disulfide powder after gold adsorption was a mixture of nm-sized molybdenum disulfide particles ( _MoS2 ) and zero valent gold.
Furthermore, in Example 2, the XPS of the molybdenum disulfide powder after gold adsorption was measured at three points. As shown in FIG. 6 , the average value of the peak top at Au 4f _7/2 was 84.4 eV, confirming that the valence of gold adsorbed to the molybdenum disulfide powder was 0.

In Example 3, when 10 mg of the molybdenum disulfide powder of Synthesis Example 1 was used and the amount of molybdenum disulfide powder added was reduced, the gold concentration in the solution after 24 hours was less than 0.1 ppm and the amount of gold adsorption was 2.35 (g/g). This shows that gold can be adsorbed up to the detection limit with a small amount of molybdenum disulfide compared to Example 2, and that the gold adsorption performance is significantly higher.

In Example 4, when 5 mg of the molybdenum disulfide powder of Synthesis Example 1 was used and the amount of molybdenum disulfide powder added was further reduced, the gold concentration in the solution after 24 hours was 67 ppm, and the amount of gold adsorption was 4.03. (g/g). Compared to Example 2, gold could not be adsorbed to the detection limit after 24 hours of adsorption, but when a solution with an initial concentration of 470 ppm was used, the amount of gold adsorbed in the solution after 24 hours was about 4 g. It was found that the gold adsorption performance was much higher than that of the adsorbents described in the above patent documents.

Here, the difference in the amount of gold adsorption after 24 hours between the results of Example 1 and Example 4 will be considered. The commercially available molybdenum disulfide powder used in Example 1 is molybdenum disulfide having a 2H crystal structure of 99% or more. The median diameter D ₅₀ measured by a dynamic light scattering particle size distribution measuring device is 13,340 nm. On the other hand, the molybdenum disulfide powder of Synthesis Example 1 used in Example 4 is molybdenum disulfide containing a 2H crystal structure and a 3R crystal structure. The median diameter D ₅₀ measured by a dynamic light scattering particle size distribution measuring device is 170 nm. The amount of gold adsorption after 24 hours in Example 1 is 0.006 g/g, while the amount of gold adsorption after 24 hours in Example 4 is extremely high at 4.03 g/g. It is presumed that this is due to the fact that the molybdenum disulfide powder of Synthesis Example 1 contains a 2H crystal structure and a 3R crystal structure and that the median diameter D ₅₀ is 170 nm. Therefore, for example, even if a molybdenum disulfide powder has a 2H crystal structure of 99% or more and a median diameter _D50 of about 170 nm, it is believed to exhibit a relatively high gold adsorption amount. Also, even if a molybdenum disulfide powder contains a 2H crystal structure and a 3R crystal structure and has a median diameter _D50 of about 13,340 nm, it is believed to exhibit a relatively high gold adsorption amount.

On the other hand, in Comparative Example 1, when carbon was used as the adsorbent, the gold concentration in the solution after 24 hours was 555 ppm and the amount of gold adsorption was 0.006 (g/g), which was equivalent to the amount of gold adsorption in Example 1, in which commercially available molybdenum disulfide powder was used as the adsorbent.

[Evaluation of low concentration precious metal (gold) adsorption]
Example 5
A gold solution of about 5 ppb was prepared using a 1000 ppm gold standard solution (manufactured by Nacalai Tesque). 400 mg of the molybdenum disulfide powder obtained in Synthesis Example 1 was added as an adsorbent to 40 g of this solution, and the solution was stirred for 5 days. As a control experiment, a solution without the addition of an adsorbent was stirred to obtain the initial concentration. A mass spectrometer (ICP-MS Agilent 8900, manufactured by Agilent Technologies) was used to measure the concentration. The results are shown in Table 3.

From the results in Table 3, in Example 5, when a gold solution with an initial concentration of 4.28 ppb was used, the gold concentration after 5 days was less than 0.01 ppb. Therefore, when using the molybdenum disulfide powder obtained in Synthesis Example 1, it is possible to use very low concentration gold solutions, such as gold solutions discharged from urban mines, gold solutions from plating waste liquid, seawater, volcanic hot water, etc. It has been discovered that gold can be recovered from gold solutions collected from nature.

[Recovery of gold after adsorption]
Example 6
100 mL of 1000 ppm gold standard solution (manufactured by Nacalai Tesque, Inc.) was used (100 mg of actual gold) and diluted with 100 mL of ion-exchanged water. 50 mg of the molybdenum disulfide powder obtained in Synthesis Example 1 was added to this diluted solution as an adsorbent, and the mixture was stirred for 24 hours to adsorb the gold. After the adsorption was completed, the molybdenum disulfide particles were filtered out.
The filtered molybdenum disulfide particles were washed twice with 20 mL of nitric acid 1.40 (Kanto Chemical Co., Ltd.) to dissolve only molybdenum disulfide. The precipitate was then washed with ion-exchanged water to obtain 75.8 mg of yellow powder. When the obtained yellow powder was subjected to XRD measurement, it was confirmed that the peak top of gold coincided with that of gold as shown in Figure 7, and the recovered yellow powder was gold (0 valence). The gold recovery rate was 76%.
In addition, the composition of the recovered yellow powder was analyzed using an X-ray fluorescence analyzer (Rigaku Corporation, Primus IV), and the gold content was found to be 99.7% by mass. Gold with a content of more than 99.0% by mass can be easily refining to produce pure gold.

<Example 7>
Instead of washing with nitric acid in Example 6, the filtered molybdenum disulfide particles were placed in a crucible and heated at 900° C. for 4 hours in an air atmosphere to obtain 88.8 mg of yellow powder. When the obtained yellow powder was subjected to XRD measurement, the peak top coincided with that of gold as shown in FIG. 7, so it was confirmed that the recovered yellow powder was gold (zero valence). The gold recovery rate was 89%, which was higher than in Example 6. The reason why the gold recovery rate in Example 6 was about 80% is that the scale of the experiment was small, as well as the fact that fine particles of molybdenum disulfide adhered to the container during the cleaning process and could not be removed. Examples include the fact that the particles are collected by filter paper when they are collected separately, and the fine particles cannot be collected because they do not precipitate sufficiently. On the other hand, the recovery method of Example 7 is considered to be superior to the recovery method of Example 6 because there is no adhesion to containers or filter paper, and there is no gold that does not settle and become unrecovered.
When the composition of the yellow powder recovered in Example 7 was analyzed using a fluorescent X-ray analyzer (Primus IV, manufactured by Rigaku Corporation), the gold content was found to be 99.2% by mass.

[Evaluation of gold adsorption on molybdenum disulfide particles with large specific surface area]
Example 8
The remaining gold concentration in the sample solution after 24 hours and the amount of gold adsorbed per gram of adsorbent after 24 hours were calculated in the same manner as in Example 4, except that the amount of molybdenum disulfide powder added in Synthesis Example 2 was changed to 4.5 mg. The results are shown in Table 4.

From the results in Table 4, in Example 8, when 4.5 mg of the molybdenum disulfide powder of Synthesis Example 2 was used, the gold concentration in the solution after 24 hours was less than 0.1 ppm, and the amount of gold adsorbed was 5.17 g/ g, and it was confirmed that the gold adsorption performance was higher than that of the molybdenum disulfide powder of Synthesis Example 1 used in Example 4.

[Gold adsorption evaluation by liquid passage test]
<Example 9>
A 1000 ppm gold standard solution (manufactured by Nacalai Tesque) was diluted with ion-exchanged water to prepare a diluted solution such that the initial gold concentration was 100 ppm.
The obtained diluted solution was fed at a rate of 3.6 mL/min and passed through a column having an internal volume of 3.6 cm ³ filled with the molybdenum disulfide powder of Synthesis Example 1. The filling amount of molybdenum disulfide powder is 3.6 ^cm3 .
The diluted solution that had passed through the column was sampled, and the gold concentration remaining in the sampled solution was quantified using an ICP optical emission spectrometer (ICP-OES, PerkinElmer, Optima 8300). The gold concentration detection limit of ICP-OES at this time is 0.1 ppm.

The gold adsorption evaluation results from this liquid passage test are shown in FIG. The horizontal axis of the figure shows the amount of liquid treated in the column, which is defined as the total amount of liquid passed (l)/molybdenum disulfide filling amount (lr). This horizontal axis is called the processing liquid amount (unitless). Moreover, the vertical axis of the figure shows the gold concentration remaining in the sampling solution, which is called the gold ion leakage concentration.

Since the gold ion leakage concentration when the treated liquid volume was up to 1070 was below the detection limit of ICP-OES, it was confirmed that the gold concentration remaining in the sampling solution was less than 0.1 ppm.

Although the gold concentration remaining in the sampling solution gradually increases after the treatment liquid volume reaches 1,430, even at treatment liquid volume 3,410 the remaining gold concentration is only 7.3 ppm, and it was confirmed that 92.7 ppm was adsorbed onto the molybdenum disulfide powder.

When recovering gold from urban mines or plating wastewater, or from gold-containing wastewater discharged in a gold ore refining process, a solution containing gold is continuously passed through a column packed with a precious metal (gold) adsorbent as in this embodiment, and the gold is adsorbed and recovered. Therefore, it can be said that the precious metal (gold) adsorbent of the present invention is suitable for recovering gold from urban mines or plating wastewater, or from gold-containing wastewater discharged in a gold ore refining process.

[Evaluation of gold adsorption in seawater]
<Example 10>
A 1000 ppm gold standard solution (manufactured by Nacalai Tesque) was diluted with simulated seawater to prepare a diluted solution such that the initial gold concentration was 100 ppt.
Simulated seawater is 24.53g of NaCl, 5.20g of _MgCl2 , 4.09g of _Na2SO4 , 1.16g of _CaCl2 , 0.695g of KCl, and _NaHCO3 in 1 liter _of ion exchange water. 0.201 g of KBr, 0.101 g of KBr, 0.027 g of H ₃ BO ₃ , 0.025 g of SrCl ₂ and 0.003 g of NaF were dissolved, and after dissolving, an aqueous NaOH solution was added to adjust the pH to 8. By adjusting to 1, the composition and pH were equivalent to seawater.
200 g of the obtained diluted solution was placed in a polyethylene test tube, 200 mg of the molybdenum disulfide powder of Synthesis Example 1 was added as an adsorbent, and the mixture was stirred at a rotation speed of 15 rpm using an overturning rotary stirrer (Rotor Mix RKVSD, manufactured by Towarabo Co., Ltd.). , and stirred for 168 hours.
After 168 hours of stirring, filtration was performed using a 0.2 μm syringe filter, and the remaining gold concentration in the sample solution was measured using a triple quadrupole inductively coupled plasma mass spectrometer (ICP-MS/MS) (Agilent). It was quantified using Agilent 8900 (manufactured by Technology Co., Ltd.). The gold concentration detection limit of ICP-MS/MS at this time is 30 ppt. The results are shown in Table 5.

From the results in Table 5, it was confirmed that in Example 10, the gold concentration remaining in the solution after 168 hours was below the detection limit of ICP-MS/MS, and was therefore less than 30 ppt. Therefore, at least 70 ppt of gold is adsorbed and recovered.

The concentration of gold contained in seawater is on the order of ppt (parts per trillion). From the results of Example 10, it can be said that the precious metal (gold) adsorbent of the present invention is suitable for adsorbing and recovering ppt-order gold from seawater. It is also considered to be suitable for recovery from solutions containing low concentrations of gold that are naturally discharged, such as volcanic hydrothermal fluids, not limited to seawater.

The precious metal adsorbent of the present invention has a high adsorption performance for precious metals, and therefore can be suitably used as a precious metal recovery material when recovering precious metals from urban mines, plating waste liquid, gold-containing waste liquid discharged in a gold ore refining process, or gold-containing solutions discharged naturally such as seawater or volcanic hot water, etc. In particular, since the adsorption performance for gold is remarkably excellent, the adsorbent can be particularly suitably used as a gold recovery material from solutions containing gold at high to very low concentrations.
Furthermore, the precious metal recovery method and precious metal adsorbent regeneration method of the present invention enable the recovery of precious metals and the regeneration of precious metal adsorbents to be easily performed, thereby reducing the environmental burden and suppressing the consumption of metal resources, and are therefore extremely useful as methods for recovering precious metals from the sea, rivers, waste, etc.

REFERENCE SIGNS LIST 1 Manufacturing device 2 Firing furnace 3 Cooling pipe 4 Recovery device 5 Exhaust port 6 Opening adjustment damper 7 Observation window 8 Exhaust device 9 External cooling device

Claims (7)

A method for recovering gold by adsorbing gold onto a noble metal adsorbent containing a metal sulfide composed of molybdenum disulfide particles , and then recovering the gold by dissolving the noble metal adsorbent in an oxidizing solution. Gold recovery , in which gold is adsorbed on a noble metal adsorbent containing a metal sulfide composed of molybdenum disulfide particles , and then the gold is recovered by heating and volatilizing the noble metal adsorbent in the presence of oxygen. Method. The method for recovering gold according to claim 1 or 2 , wherein the median diameter _D50 of the molybdenum disulfide particles determined by dynamic light scattering is 10 nm or more and 1000 nm or less. The gold recovery method according to claim 1 or 2 , wherein the primary particles of the molybdenum disulfide particles have a disk-like, ribbon-like, or sheet-like shape and a thickness in the range of 3 to 100 nm. The specific surface area of the molybdenum disulfide particles, as measured by the BET method, is 10 m ² /g or more.
3. The method for recovering gold according to claim 1 or 2 . 3. A method for regenerating a precious metal adsorbent, comprising recovering molybdenum oxide volatilized by the precious metal recovery method according to claim 2, and then sulfurizing the molybdenum oxide to regenerate a precious metal adsorbent composed of molybdenum disulfide particles . The median diameter _D50 of molybdenum disulfide constituting the noble metal adsorbent determined by a particle dynamic light scattering method is 10 nm or more and 1000 nm or less,
The shape of the primary particles is disc-shaped, ribbon-shaped, or sheet-shaped,
The thickness is in the range of 3 to 100 nm,
and the specific surface area measured by the BET method is 10 m ² /g or more,
The gold recovery method according to claim 1 or 2, wherein the gold recovery method is performed after adsorbing 0.56 g or more of gold per 1 g of the noble metal adsorbent.

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